Effect of substrate type on population dynamics and growth of coral reef sponges in Torres Strait (CRC-TS Project: Task Number T1.6a)

Full description

The influence of substrate type on the ecology of the sponges Coscinoderma matthewsi and Hyrtios erecta was examined on the coral reefs at Masig Island and Kodall Island, in central Torres Strait.Twelve 4 m² permanent quadrats, located 2-40 m apart, were established at each reef on the reef slope (30-50°) at depths between 10 and 12 m. Six quadrats at each island were dominated by rock (>=66% of the seafloor). The other 6 quadrats at each island were dominated by rubble (>=66% of the seafloor). The remaining substrate in each quadrat consisted mostly of sand or was occupied by living organisms such as hard and soft coral species.Quadrats were surveyed every 3-5 months for a period of 27 months (December 2004 to March 2007). At the start of the study, each quadrat had between 0-3 individuals of Coscinoderma matthewsi and Hyrtios erecta. During each survey, each quadrat was thoroughly checked for the presence of Coscinoderma matthewsi and Hyrtios erecta and the position of each sponge marked on gridded data sheets. Sponges that moved out of the quadrat, were not counted even if they were found alive a short distance away.The effect of substrate type on sponge growth was examined by measuring the volume of 27 Coscinoderma matthewsi and 30 Hyrtios erecta individuals attached to either rock or rubble at Kodall and Masig Islands, using a photographic method. For Coscinoderma matthewsi, a close-up photo was taken looking directly down, thus sponge length and width could be accurately determined. For Hyrtios erecta, photos of individuals were taken along their full length including any branches; if needed several photos from different angles were taken so that length of all branches could be calculated.The tagged sponges were measured each time quadrats were surveyed. Sponges were also measured if they moved out of the quadrat area. Water temperature was recorded using HOBO Water Temp Pro recorders, deployed at a depth of 10 m at Kodall and Masig Islands. Data on wind direction and speed was obtained from the Australian Government's Bureau of Meteorology (www.bom.gov.au) weather station at neighbouring Poruma (Coconut) Island, approximately 50 km away. For each month, the number of days where wind direction was NE, N and NW and wind strength was >50 km/h were counted.
Rock and rubble are common substrates on coral reefs in Torres Strait, constituting upwards of 70% of the benthic cover. Rubble is typically unbound or unstable in Torres Strait, being moved around by storms and daily water action driven by currents or wind. This study was initiated to determine if there were differences in the population dynamics and growth of Coscinoderma matthewsi and Hyrtios erecta on rock or rubble substrates in central Torres Strait within and between years.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Statement: A non-destructive method of measuring sponge size involves photographing individuals next to a ruler to provide a scale, with size measured using image analysis. See:de Caralt S, Uriz MJ, Wijffels RH (2008) Grazing, differential size-class dynamics and survival of the Mediterranean sponge Corticium candelabrum. Mar. Ecol. Prog. Ser. 360: 97-106.Duckworth AR, Battershill CN (2001) Population dynamics and chemical ecology of New Zealand Demospongiae Latrunculia sp. nov. and Polymastia croceus (Poecilosclerida: Latrunculiidae: Polymastiidae). NZ. J. Mar. Freshw. Res. 35: 935-949.Sponge volume, which can be calculated by the formula that best represents the gross morphology (e.g. cylinder) is a good estimate of sponge weight. See:Duckworth AR, Battershill CN (2003) Sponge aquaculture for the production of biologically active metabolites: the influence of farming protocols and the environment. Aquaculture 221: 311-329.For Coscinoderma matthewsi, a close-up photo was taken looking directly down, thus sponge length and width could be accurately determined. Only Coscinoderma matthewsi individuals that had a roundish or oblong shape were used to obtain good volume estimates. When sponges were buried under rubble, rubble pieces were temporarily moved to photograph the sponge. Individual volume was calculated using the formulae for a half prolate-spheroid:Volume = (4/3 pi a b²)/2where 'a' represents half the length measurement and 'b' represents half the width measurement. See:Crawshay LR (1939) Studies in the market sponges. I. Growth from the planted cutting. J. Mar. Biol. Assoc. U. K. 23, 553-574.Length and width were measured to the nearest 0.5 cm, with volume given as cm³. For Hyrtios erecta, photos of individuals were taken along their full length including any branches; if needed several photos from different angles were taken so that length of all branches could be calculated. Average width was determined by measuring the thickness at 3 places along the sponge's length. Branch lengths and widths were measured to the nearest 0.5 cm. Individual volume was calculated by considering each branch to be a cylinder, a formulae used for other branching species. See:Koopmans M, Wijffels RH (2008) Seasonal growth rate of the sponge Haliclona oculata (Demospongiae: Haplosclerida). Mar. Biotechnol. 10, 502-510.Wind direction and speed is assumed to be similar between Poruma and the study area considering the short distance across open water. Because the study sites at Kodall and Masig Islands are north facing, only NE, N and NW winds >50 km/h (near gale force and greater) were considered to possibly impact the ecology of the two sponge species.

Notes

Credit
Duckworth, Alan R, Dr (Principal Investigator)